U.S. patent number 4,664,769 [Application Number 06/791,666] was granted by the patent office on 1987-05-12 for photoelectric enhanced plasma glow discharge system and method including radiation means.
This patent grant is currently assigned to International Business Machines Corporation. Invention is credited to Jerome J. Cuomo, Charles R. Guarnieri.
United States Patent |
4,664,769 |
Cuomo , et al. |
May 12, 1987 |
Photoelectric enhanced plasma glow discharge system and method
including radiation means
Abstract
Plasma enhancement is achieved in a plasma glow system by
increasing the number of photoelectric electrons in the plasma glow
by producing photoelectrons from the surface of a target in the
system by the use of a radiation source. This is more particularly
accomplished by flooding the surface of the target with a UV laser
beam during the plasma process where emitted photoelectrons are
injected into the plasma to increase the plasma density. The plasma
enhancement is used in a sputter etching/deposition system which
includes a chamber containing a cathode, a target, a substrate
platform containing substrate and a pump. An ultraviolet light
source such as a UV laser and focussing optics for focussing the UV
radiation onto the target through a UV transmission window are also
provided. A plasma region in the chamber is enhanced by photons
from the laser striking the target and producing photoelectrons
which are injected into the plasma to increase its density.
Inventors: |
Cuomo; Jerome J. (Lincolndale,
NY), Guarnieri; Charles R. (Somers, NY) |
Assignee: |
International Business Machines
Corporation (Armonk, NY)
|
Family
ID: |
25154418 |
Appl.
No.: |
06/791,666 |
Filed: |
October 28, 1985 |
Current U.S.
Class: |
204/192.1;
204/192.12; 204/298.31; 250/425; 427/570; 427/572; 204/192.11;
204/192.34; 250/423P; 427/526 |
Current CPC
Class: |
G21B
1/23 (20130101); H01J 37/32321 (20130101); Y02E
30/10 (20130101) |
Current International
Class: |
H01J
37/32 (20060101); H05H 1/22 (20060101); H05H
1/02 (20060101); C23C 014/00 () |
Field of
Search: |
;250/423P,425
;204/298,192.1,192.11,192.12,192.31,192.34 |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
Townsend, "Photon-Induced Sputtering"; Surface Science 90(1979) pp.
256-264. .
Laser-Plasma Interactions for the Deposition and Etching of
Thin-Film Materials P. J. Hargis, Jr. et al.--Solid State
Technology Nov. 1984 pp. 127-133. .
Plasma-Initiated Laser Deposition of Polycrystalline and
Monocrystalline Silicon Films J. M. Gee et al., Mat. Res. Soc.
Symp. Proc. vol. 29, (1984) published by Elsevier Science
Publishing Co., Inc. pp. 15-20. .
Laser-Induced Plasmas for Primary Ion Deposition of Epitaxial Ge
and Si Films D. Lubben et al., J. Vac. Sci. Technol. B 3 (4)
Jul/Aug. 1985 pp. 968-974. .
Laser Photoelectron Sources of High Apparent Brightness Gail A.
Massey IEEE Journal of Quantum Electronics vol. QE-20 No. 2 Feb.
1984 pp. 103-105..
|
Primary Examiner: Demers; Arthur P.
Attorney, Agent or Firm: Goodwin; John J.
Claims
Having thus described our invention, what we claim as new and
desire to secure by Letters Patent is:
1. In a plasma system of the type including a chamber containing
plasma glow discharge, a means for adding electrons to said plasma
to increase the intensity of said plasma glow discharge including a
target, a source of photons directed onto said target for producing
photoinduced photoelectrons which are emitted from said target and
injected into said plasma.
2. A plasma system according to claim 1 wherein said system further
includes a chamber containing said target, a substrate holder and
substrates thereon subject to etching or deposition processing, and
a sputtering gas in said chamber.
3. A plasma system according to claim 1 wherein said source of
photons is a beam of electromagnetic radiation directed onto said
target.
4. A plasma system according to claim 2 wherein said beam of
electromagnetic radiation is an ultraviolet light source located
within said chamber.
5. A plasma system according to claim 2 wherein said beam of
electromagnetic radiation is an ultraviolet light source located
external to said chamber.
6. A plasma system according to claim 3 wherein said ultraviolet
light source is a continuous light source.
7. A plasma system according to claim 4 wherein said ultraviolet
light source is a continuous light source.
8. A plasma system according to claim 3 wherein said ultraviolet
light source is a pulsed light source.
9. A plasma system according to claim 4 wherein said ultraviolet
light source is a pulsed light source.
10. A plasma system according to claim 6 wherein said ultraviolet
light source is a laser.
11. A plasma system according to claim 2 wherein said beam of
electromagnetic radiation is directed onto said target in a given
image pattern, and wherein said photoelectrons are emitted from
said target in a corresponding image pattern.
12. A method for enhancing the intensity of a plasma glow in a
chamber by adding electrons to said plasma glow comprising:
the step of forming a plasm glow region in said chamber using a
glow discharge diode structure including a cathode and a target,
and
the step of directing ultraviolet radiation onto said target to
generate photoelectrons which are injected into said plasma glow
region to enhance the plasma density of said glow.
13. A method according to claim 12 wherein the step of directing
ultraviolet radiation onto said target is carried out by directing
a UV laser beam from a UV laser onto said target.
14. A method according to claim 12 wherein said chamber includes a
specimen and said method includes the step of providing a
sputtering gas in said chamber and said plasma glow functions to
effect an etching or deposition process on said specimen.
15. A method according to claim 13 further including the step of
forming said laser beam into a given pattern on said target.
16. A method according to claim 12 wherein the energy of said
ultraviolet radiation is selected to be less than the work function
of said target to provide non-linear multiphoton effects.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to glow discharge systems and
methods, and more particularly, to increasing the amount of
electrons in the plasma glow region of a glow discharge system by
radiation by photons such as by using a laser beam to enhance the
intensity of the glow for improved etching/deposition
processes.
2. Description of the Prior Art
The prior art contains references wherein radiation such as by
laser beams are used in combination with plasmas for various
diverse purposes.
U.S. Pat. No. 3,723,246 issued Mar. 27, 1973 to Lubin, entitled
PLASMA PRODUCTION APPARATUS HAVING DROPLET PRODUCTION MEANS AND
LASER PRE-PULSE MEANS describes an apparatus and method for
producing a freely expanding high temperature plasma from a high
density target that is irradiated with laser light by a tailored
laser pulse. Means are described for producing a tailored laser
light pulse and a tailored target for producing a laser-target
interaction.
U.S. Pat. No. 3,826,996 issued July 30, 1974 to Jaegle et al
entitled METHOD OF OBTAINING A MEDIUM HAVING A NEGATIVE ABSORPTION
COEFFICIENT IN THE X-RAY AND ULTRAVIOLET SPECTRAL RANGE AND A LASER
FOR PRACTICAL APPLICATION OF SAID METHOD, a plasma is formed from a
material in which the ions possess discrete metastable energy
states interacting with the energy states of the continuum which
are populated by the free electrons of the plasma. Population
inversion is achieved between a number of these metastable states
and states of lower energy, negative absorption being then produced
for the transition which couples the metastable states with said
states of lower energy.
In order to form the plasma, a giant-pulse laser beam is caused to
interact in vacuum with a solid target formed of said material and
is focused within the target near the surface through which the
beam passes, the beam power being such as to ensure sufficiently
populated metastable states of the ions of the material.
U.S. Pat. No. 4,152,625 issued May 1, 1979 to Conrad, entitled
PLASMA GENERATION AND CONFINEMENT WITH CONTINUOUS WAVE LASERS
describes a method and apparatus for initiating a stable plasma and
maintaining the plasma stationary. A high power, continuous wave
laser is used to initiate and maintain the plasma, while a magnetic
trap confines the plasma.
In U.S. Pat. No. 4,189,686 issued Feb. 19, 1980 to Brau et al
entitled COMBINATION FREE ELECTRON AND GASEOUS LASER describes a
multiple laser having one or more gaseous laser stages and one or
more free electron stages. Each of the free electron laser stages
is sequentially pumped by a microwave linear accelerator.
Subsequently, the electron beam is directed through a gaseous
laser, in the preferred embodiment, and in an alternative
embodiment, through a microwave accelerator to lower the energy
level of the electron beam to pump one or more gaseous lasers. The
combination laser provides high pulse repetition frequencies, on
the order of 1 kHz or greater, high power capability, high
efficiency, and tunability in the synchronous production of
multiple beams of coherent optical radiation.
The publication LASER-PLASMA INTERACTIONS FOR THE DEPOSITION AND
ETCHING OF THIN-FILM MATERIALS by Philip J. Hargis, Jr. and James
M. Gee, Solid State Technology/Nov. 1984, pp. 127-133, states that
laser-plasma chemical processing is a new materials processing
technique in which both ultraviolet laser irradiation and a glow
discharge are required for deposition or etching. This versatile
materials processing technique was used to deposit silicon and etch
a number of insulators. The process was also used to deposit
epitaxial silicon films on single-crystal silicon wafers. Deposited
and etched films were characterized by laser Raman spectroscopy,
transmission electron microscopy, and scanning electron microscopy.
Results obtained to date have been interpreted in terms of a
mechanism that involves interaction of the incident ultraviolet
laser radiation with a plasma deposited absorbed layer on the
substrate.
In an other publication by J. M. Gee, P. J. Hargis, Jr., M. J.
Carr, D. R. Tallant and R. W. Light entitled PLASMA-INITIATED LASER
DEPOSITION OF POLYCRYSTALLINE AND MONOCRYSTALLINE SILICON FILMS,
Mat. Res. Soc. Symp. Vol. 29 (1984) published by Elsevier Science
Publishing Co., Inc., the authors report a new method of silicon
deposition using the interaction between the radiation from a
pulsed-ultraviolet excimer laser and the plasma species produced in
a glow discharge in silane (SiH.sub.4). Examination of the
deposited film by laser Raman spectroscopy and by transmission
electron microscopy revealed that the morphology ranged from
polycrystalline silicon at laser fluences of 0.13-0.17 J/cm.sup.2
to epitaxial silicon at fluences of 0.4-0.6 J/cm.sup.2. Growth
rates of 100 nm/min for polycrystalline silicon and 30 nm/min for
monocrystalline silicon were achieved.
The Hargis and Gee publication and Gee et al publication, referred
to above, do not anticipate the present invention. Both of these
papers cover the same work on photo enhanced chemical vapor
deposition. Their work shows the laser radiation interacts with an
absorbed layer deposited by the plasma. They also show the laser
radiation does not interact with the plasma. The electron-hole
plasma discussed in their paper exists in the deposited layers
only. It is a change in the electronic distribution of the solid
that drives a chemical reaction.
A very recent publication, LASER-INDUCED PLASMAS FOR PRIMARY ION
DEPOSITION OR EPITAXIAL Ge AND SL FILMS (J. Vac. Sci. Technol. B.
Jul./Aug., 1985, pp. 968-974) is also of interest but does not
anticipate the present invention. Lubben et al use the material
ablated by laser radiation to deposit a film. They discuss the
generation of the neutral plasma caused by the interaction of the
laser radiation with the ablated material. The present invention
deals with the enhancement of a plasma by the generation of
photoelectrons using UV radiation.
In the publication by Gail A. Massey entitled "Laser Photoelectron
Sources of High Apparent Brightness", published in IEEE Journal of
Quantum Electronics, Vol., QE20, No. 2, Feb. 1984, the author
states that by focusing an ultraviolet laser beam to a small spot
on an appropriately shaped cathode, one can obtain photoelectron
beams of increased brightness. Such a continuous electron source
may be useful in electron beam lithography and other
applications.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a method and
structure to enhance the plasma density of a plasma glow
region.
Another object of the present invention is to provide a method and
structure to enhance the plasma density of a plasma glow region by
producing photoelectrons from the surface of a target.
Another object of the present invention is to provide a method and
structure to enhance the plasma density of a glow region by adding
electrons to the glow by directing photons onto a target to release
photoelectrons.
A further object of this invention is to provide a method and
apparatus to produce photon energy directed onto a target surface
to release electrons into a plasma glow.
Still another object of the present invention is to provide laser
apparatus for directing laser radiation onto a target for releasing
electrons into a plasma glow.
The foregoing and other objects, features and advantages of the
invention will be apparent from the following more particular
description of the invention as illustrated in the accompanying
drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic diagram of an embodiment of the structure
according to the principles of the present invention.
FIG. 2 is an illustration of a curve showing the relationship of
photoelectric current within a plasma glow vs the photon intensity
of the glow using the present invention.
DESCRIPTION OF THE INVENTION
The significant feature of the present invention is that a novel
approach for increasing the plasma density of a glow region is
accomplished by providing a means to impart energy to a target
surface. The energy so introduced is transferred to the target
material and causes electrons to be released and free to enter the
plasma glow where they will in turn produce ions.
Glow discharge diode systems derive their primary electron source
from secondary electrons due to ion, photon and electron
bombardment of target surfaces. These electrons feed the glow
region where they are accelerated producing ions which further
amplify their numbers. Any processes that add electrons to the
plasma glow region will enhance the intensity of the glow. For
example, high secondary emission surfaces produce plasma densities
that are much higher than materials with low secondary electron
emission coefficients. Electron injection into plasmas form an
independent electron source and will also increase the plasma
density (i.e., triode sputtering.)
In the present invention, plasma enhancement is achieved by
increasing the number of photoelectric electrons from the surface
of a target by the use of a photon source whose energy is greater
than the work function of the surface it is impinged upon. The
number of electrons is a function of the intensity proportional to
a function of the intensity of the light source. Therefore, the
more intense the photon source, the more electrons will be emitted
from the surface. Although other sources are applicable, a laser is
an ideal source of photon due to its intensity and directivity.
Thus, UV laser with wavelengths in the deep UV. This is
accomplished by flooding the surface of the target with UV light
during the plasma process where the photoinduced electrons will be
injected into the plasma. This is shown in FIG. 1.
Referring to FIG. 1, a sputtering system 1 is shown including a
cathode 2, a target 3, an insulator 4 for the cathode 2, a
substrate platform 5 containing substrate 6, a pump 7, an
ultraviolet light source 8 such as a UV laser, focussing optics for
focussing the UV radiation onto the target material through a UV
transmissive window 10, a plasma region 11, a typical sputtering
ion 12, a typical ion induced secondary electron, a typical UV
photon and a typical photoelectron.
The sputtering system is operated in the same conventional manner
as one skilled in sputtering would operate it to obtain the desired
material properties. A substrate bias is used as required by
material considerations. Sputtering gas is employed as required by
material considerations, for example, Ar or a reactive gas such as
oxygen or mixtures (includes all gases). Cathode power supply can
be either dc or rf. With insulating targets the supply must be rf.
In order to enhance the plasma, the energy of the photons provided
by source 8 must be greater then the work function of the target 3
material. Some particular examples are:
______________________________________ photon energy target
material greater than ______________________________________ Al 4.4
eV Cu 4.9 eV Cu <110> 5.6 eV Pt 5.5 eV Ti 4.5 eV oxides of Ti
3.7 eV oxides of Zr 3.9 eV
______________________________________
The invention is not limited to the above-listed materials and
energies, however.
The electrons anticipated are about lmA/cm.sup.2 per/10 ns pulses.
This will produce an intense plasma enhancement. The calculated
values are for an estimated efficiency of 10.sup.-4 electrons per
incident 6.5 eV photon.
It should also be noted that this will produce an intense pulsed
ion beam bombarding the target and a pulsed flux of material
depositing on the substrate. With materials that generate negative
ions, an intense pulsed particle beam is also expected. Thus, a
patterned photon beam will produce pulsed patterned deposition or
etching.
Electron burst are obtainable that far exceed the calculated
values, for example, current densities are realized of about 2
amps/cm.sup.2. FIG. 2 shows the amplitude for the cathode current
vs photon intensity (fluence) in a dc diode sputtering system. The
measurements with and without a plasma are shown. In both cases,
the current increases linearly with fluence until saturation
(probably due to space charge) is reached. The discrepancy between
experiment and calculated values could be attributed to an error in
the estimated photoelectric efficiency or because the amplification
effects due to plasma enhancements are dominant. The use of a high
intensity, continuous UV light source will significantly increase
the enhancement. It should be noted that the photoelectric current
in the curves in FIG. 2 levels off for lower voltage, but does not
level off for higher voltage. If the photoelectric current produced
is plotted against time, it could be seen that the effect of the
photon beam is not initially observed, but that after a given time
period, the effects are noted. The shape or configuration of such
curve over such time period is useful to one skilled in the art
because it indicates the effects of the photoelectrons in the
plasma.
It is important to note that althou9h the system of FIG. 1 used a
UV laser beam, it is not the only embodiment that can be used. For
example, it is not necessary that the means for producing the
photons which are directed onto the surface of target 3, be located
external to the system 1. The photon source may be an internally
located UV source as well as an external source. The photon source
may be a continuous (UV et al) source or a pulsed source. The
particular embodiment selected by one skilled in the art would
depend on the application of the system. The system can be widely
employed for etching and for deposition. Also, as the
photoelectrons are released from the target 3, they may have
potentials of 1,000 eV and thus, move directly through ground
potential plasma glow without scattering or dispersing.
Thus, if the photons were directed onto the largest surface 3 in a
particular pattern, for example, through a laser mask, to produce a
patterned photon beam, then the released photoelectrons would have
the same configuration as they leave the target surface and the
system could be used by one skilled in the art for patterning.
Still another feature of the invention is that non-linear photon
effects may be obtained. This is achieved by selecting the energy
of the radiation beam, for example the UV beam from laser 8 in FIG.
1, to be less than the work function of the irradiated target, such
as target 3 of FIG. 1.
* * * * *